feat(opal26): #1's head trim is now a measured number, and candidates get their own room

Two changes to the ear-boundary ground truth, kept deliberately distinct.

#1 was the last GO with an unfinished instruction — PLN said "trim leading
silence tho" without an amount. The amount is now measured rather than
estimated: every sample is EXACTLY zero up to sample 64038 (1.452109 s @
44.1 kHz), and the first audible frame peaks at -28 dBFS. That is a sample-exact
scan, not a threshold and not a detector, which is why it is allowed into a file
whose header forbids detector output. Recorded as start=1.45, keeping a ~2 ms
guard so the first transient cannot be clipped, with the full measurement and
method stored alongside it for audit.

#11 and #12 gain machine PROPOSALS in a new `candidates` block, structurally
separate from `verified` so nothing can be mistaken for a confirmed boundary.
On the two boundaries that also have ear answers, the `takeover` estimate landed
within 0.7 s (#8 2726.25 vs 2726.4, #10 3268.3 vs 3269.0) — which is a reason to
audition takeover first, not a reason to trust it: n=2, on the cases that were
already easy.

#13 and #15 are listed with an explicit NO CANDIDATE and the reason, so a future
reader does not go looking for numbers that cannot exist: zero voting orbits
across three gates and two estimators, because those transitions share their
sounds and a timbral lens is blind to them by construction.

armada/tide-table/judge_specs/opal26_boundaries_ear.json

@@ -45,8 +45,16 @@
       "alt_note": "0:10.9 — only if we craft our own crossfade"
     },
     "1": {
-      "start": null,
-      "note": "GO, but 'trim leading silence tho' — head trim needed, exact amount not yet measured"
+      "start": 1.45,
+      "note": "GO, but 'trim leading silence tho' (PLN). The amount is now MEASURED, not detected: the head is literal digital silence — every sample is exactly zero up to sample 64038 (= 1.452109 s @ 44.1 kHz), and the first audible frame peaks at -28 dBFS. Cutting at 1.45 keeps a ~2 ms guard before the first transient so the attack cannot be clipped.",
+      "measured": {
+        "first_nonzero_sample": 64038,
+        "first_nonzero_s": 1.452109,
+        "all_zero_before": true,
+        "source": "tracks_v4_streaming/01 - Ceci n'est pas Une Bombe.flac",
+        "method": "sample-exact scan; NOT a threshold and NOT a detector estimate",
+        "date": "2026-08-16"
+      }
     }
   },
   "unjudged": [
@@ -55,6 +63,46 @@
     13,
     15
   ],
+  "_candidates_comment": [
+    "UNCONFIRMED machine proposals, kept separate from `verified` on purpose —",
+    "nothing here is a boundary until PLN's ear says so. From cut_lens3 run 2",
+    "(cut_candidates_v3run2.json). On the two boundaries that also have ear",
+    "answers, u0.85/`takeover` landed within 0.7 s (#8 2726.25 vs 2726.4;",
+    "#10 3268.3 vs 3269.0) — encouraging, but that is n=2 on the cases that were",
+    "already easy, so it is a reason to audition `takeover` FIRST, not to trust it.",
+    "#13 and #15 are absent by exhaustion: zero voting orbits across three gates",
+    "and two estimators. Those two are ear-only; see cut_lens3.py's docstring."
+  ],
+  "candidates": {
+    "11": {
+      "title": "Ghosts in the Toilets",
+      "nominal": 3560.2,
+      "takeover": 3557.2,
+      "onset": 3515.7,
+      "mid": 3554.2,
+      "voters": 3,
+      "note": "all five fractions inside 3.5 s => SHORT crossfade; nominal looks ~3 s late"
+    },
+    "12": {
+      "title": "Mafia",
+      "nominal": 3681.6,
+      "takeover": 3688.1,
+      "onset": 3667.1,
+      "mid": 3680.1,
+      "voters": 3,
+      "note": "span 21 s => LONG crossfade; nominal sits mid-span, so the takeover is later than the current cut"
+    },
+    "13": {
+      "title": "Vague de CRIME",
+      "nominal": 3889.1,
+      "note": "NO CANDIDATE — timbral lens structurally blind here (shared sounds across the switch). Ear-only."
+    },
+    "15": {
+      "title": "REVOLUTION",
+      "nominal": 4547.4,
+      "note": "NO CANDIDATE — same as #13. Ear-only."
+    }
+  },
   "cut_from_release": {
     "14": {
       "title": "Desire",